Counter reset mechanism

ABSTRACT

An electromagnetically operated counter comprising a pair of radially spaced number wheels and a pair of resetting knobs mounted coaxially therewith each adapted to be individually axially depressed for resetting the respective number wheel. The number wheels are interconnected through an intermediate pinion such that when each wheel is depressed, the pinion and therefore the other wheel is locked against rotation. The knobs have teeth for positively clutching the respective wheel to the knob and a stationary tooth is adapted to cooperate with the knob teeth for ensuring the wheel is located in a full count position when the knob is released. A core and clapper subassembly of an electromagnetic operator is mounted on rearwardly extending posts of a two-piece frame for being pivotally adjusted about the axis of one of the posts to set the air gap of the clapper. A star wheel of a verge drive is mounted on a shaft supporting the lowest order counter wheel, and a verge is reciprocably mounted on the free end of the clapper for reciprocable movement along an axis transverse to the axis of the star wheel shaft and has a slot receiving the star wheel shaft for orienting the verge with respect to the star wheel.

United States Patent [151 3,644,717 Voegelin et al. 5] Feb. 22, 1972 [54] COUNTER RESET MECHANISM [72] Inventors: Howard J. Voegelin, Cheshire; Ernest G. [57] ABSTRACT v Hoffman, Middlefield; Lloyd J- P An electromagnetically operated counter comprising a pair of west Hartford of Y radially spaced number wheels and a pair of resetting knobs mounted coaxially therewith each adapted to be individually [73] Asslgnee' Veeder Industries Hartford Conn' axially depressed for resetting the respective number wheel. [22] Filed: May 7, 1970 The number wheels are interconnected through an intermediate pinion such that when each wheel is depressed, the [21] Appl' 35406 pinion and therefore the other wheel is locked against rotation. The knobs have teeth for positively clutching the respec- [52] [1.8. CI ..235/92 C, 235/92 R, 235/144 DM i wheel to t k n a i n ry th i a pt to [5 l] Int. Cl. ..G06m 1/28 cooperate h the knob teeth f r n g h h l i [58] Field of Search 235/144 DM, 144 BM, 92 C, 13; located in a full count position when the knob is released. A 58/8 5 5 core and clapper subassembly of an electromagnetic operator is mounted on rearwardly extending posts of a twopiece [56] References Ci d frame for being pivotally adjusted about the axis of one of the posts to set the air gap of the clapper. A star wheel of a verge UNITED STATES PATENTS drive is mounted on a shaft supporting the lowest order counter wheel, and a verge is reciprocably mounted on the Veeder ..235/l44 free end of the clapper for reciprocable movement along an 12/1930 axis transverse to the axis of the star wheel shaft and has a slot 3226021 10/1965 Dusinberre et al 235/92 C receiving the star wheel shaft for orienting the verge with Primary Exarru'nerMaynard R. Wilbur Assistant Examiner-Joseph M. Thesz, Jr. Attorney-Prutzman, Hayes, Kalb dc Chilton respect to the star wheel.

6 Claims, 8 Drawing Figures PATENTEDFEBZZ I912 3.644.717

SHEET 1 OF 3 5! W INVENTORS If} x HOWARD J. VOEGELIN a5 ERNEST c. HOFFMAN ATTORNEYS COUNTER RESET MECHANISM BRIEF SUMMARY OF THE INVENTION The present invention relates to improvements in counters.

It is a principal aim of the present invention toprovide a new and improved predetermining counter of the type adapted for being manually set to any selected count and having an electromagnetic operator adapted to be pulsed for indexing the counter in the subtracting direction from the selected count to zero.

It is another aim ofthe present invention to provide a new and improved meter-type counter (i.e., a counter having counter wheels mounted for rotation about spaced-parallel axes) having settable counter wheels.

It is a further aim of the present invention to provide a new and improved meter-type counter having a plurality of counter wheels each independently manually settable in either angular direction without affecting the setting of the remaining wheels.

It is another aim of the present invention to provide a new and improved manually settable counter.

It is another aim of the present invention to provide a new and improved verge-type counter-indexing mechanism.

It is a further aim of the present invention to provide a new and improved electromagnetic counter of the type employing a pivotal clapper for indexing the counter and for providing for adjustment of the clapper airgap.

It is a still further aim of the present invention to provide a new and improved predetermining counter having an economical and compact assembly of parts.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

A better understanding of the invention will be obtained from the following detailed description and the accompanying drawings of an illustrative application of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a top plan view, partly broken away and partly in section, of an embodiment of a predetermining counter incorporating the present invention;

FIG. 2 is a reduced front elevation view of the counter;

FIG. 3 is a longitudinal elevation section view, partly broken away and partly in section, of the counter taken substantially along line 3-3 of FIG. 1;

FIG. 4 is a longitudinal elevation section view, partly in section, of the counter taken substantially along line 4-4 of FIG.

FIG. 5 is an enlarged section view, partly broken away and partly in section, showing a knob mounting socket of the p'redetermining counter;

FIG. 6 is an enlarged side view of a setting knob of the predetermining counter;

FIG. 7 is a transverse section view, partly broken away and partly in section, of the counter taken substantially along line 7-7 ofFIG. 1; and

FIG. 8 is a transverse section view, partly broken away, of the counter taken substantially along line 88 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail wherein like numerals designate like parts throughout the several figures, an embodiment 10 of a predetermining counter incorporating the present invention is shown comprising a two-piece molded plastic frame 12 with stacked frame sections 14, 16 having generally parallel forward base portions 17, 18 respectively and rearwardly extending support posts 19-23 and 24-26 respectively. The rear frame section 16 is mounted on the front section posts 19-23 and the ends of the posts 19-21 are suitably staked to secure the frame sections together. The operative parts of the counter are mounted on the frame 12 as hereinafter described and the entire subassembly 27 thereby provided is mounted within a boxlike housing 28 with the base portion 17 of the frame section 14 providing the front face of the assembled unit and with the subassembly 27 secured within the housing 28 by suitable retaining rings 29 mounted on the ends of the posts 24-26.

The housing 28 has a peripheral flange 30 for mounting the counter assembly as for example within a suitable panel opening (not shown), for which purpose there is provided a rearwardly extending threaded stud 31 on the housing 28 and a U- shaped clamp 32 having an opening receiving the stud 31 and adapted to be mounted to firmly engage the inner face of the panel by a wingnut 36.

A pair of decade counter wheels 40, 42 of ascending order are mounted for rotation about spaced-parallel axes within the forward cavity of the frame between the base portions 17, 18. The lower order counting wheel 40 is keyed by a flat onto a steel shaft 44 rotatably mounted within a bore in the base portion 18, and the higher order counter wheel 42 is formed with an integral plastic shaft 46 also rotatably mounted within a bore in the base portion 18. A star wheel 48 is keyed by a flat onto the rear end of the shaft 44 for indexing the counter, and a transfer pinion 50 (FIG. 1) is rotatably mounted on a steel pin 52 extending parallel to the wheel shafts and press fit within a suitable bore in the base portion 18. For convenience of manufacture the pinion 50 is formed by two molded gear sections 53, 54 having suitable interfitting parts for interlocking the sections 53, 54 together for common rotation. The pin 52 has an enlarged outer end for holding the gear sections 53, 54 together and for positioning the pinion 50.

A leaf spring 60 engageable with a ball 62 supported in an end socket of the star wheel 48 is provided for biasing the lower order counter wheel 40 to its forward operative position shown in FIG. 3, and a similar leaf spring 64 is provided for biasing the wheel 42 to its forward operative position shown in FIG. 3. The forward operative position of the wheel 40 is established by an adjustable stop 66 for the leaf spring 60 whereas the rear face of the base portion 18 provides a stop for the leaf spring 64 for establishing the forward operative position of the wheel 42.

A pair of wheel setting knobs 68 are mounted within stepped bores 70, 71 in the frame coaxial with the shafts 44, 46. Each knob 68 has a central bore 72 which receives a light compression spring 73 and a spring supported ball 74 which engages a forward axial extension of the corresponding counter wheel to bias the knob to its forward inoperative position shown in the drawings and to retain the wheel in its operative position. Each knob has ten equiangularly spaced peripheral teeth 75, and three inwardly projecting teeth 76 (FIG. 5) are provided on the frame for being received between the teeth 75 for locking the knob 68 in one of ten angular positions (which correspond to the ten full count positions of the corresponding counter wheel) when the knob is in its forward inoperative position.

The counter wheels 40, 42 comprise numeral discs 80 retained against the wheel hubs 82, 84 by locking rings 81 and which bear the sequence of indicia of 0-9 for being selectively viewed through the windows 85, 86 in the base portion 17. A crystal 87 formed of transparent plastic is snap fitted within a generally rectangular recess 88 in the front face of the base 17 to cover the windows 85, 86. Each wheel hub 82, 84 has four axially extending projections 94 for angularly locating the indicia disc 80 relative to the wheel hub and for providing teeth adapted to be engaged by projecting knob teeth 75 for positively clutching the knob to the wheel.

Upon manually depressing each knob 68, the knob will initially compress the corresponding spring 73 to provide for positive engagement of the knob with the wheel (and to thereby lock the wheel against rotation) and then axially shift the wheel against the bias of the leaf spring 60 or 64, to provide for disengagement of the knob from the teeth 76 (and for disengaging the wheel from the pinion 50 as hereinafter described) and for thereby freeing the knob 68 for resetting the counter wheel. After the counter wheel is reset, the knob 68 may be released to permit the knob and counter wheel to be returned to their respective forward positions by the corresponding leaf spring 60 or 64 and the light compression spring 73. During such return motion the knob 68 and wheel are locked against rotation by the stationary teeth 76 well before the knob becomes disengaged from the wheel such that the teeth 76 provide for ensuring the wheel is a full count position upon reengagement with the pinion 50.

Referring to FIGS. 1 and 6 a combined wheel transfer and locking mechanism comprises the pinion 50, a pair of contiguous locking rings 100, 101 and a two-tooth gear sector 102 on the lower order counter wheel 40, and a locking ring 104 I and a 20-tooth drive gear 106 on the higher order counter wheel 42. The pinion 50 comprises a forward eight-tooth transfer gear portion 108 (provided by the molded gear section 53) and a rear four-tooth locking gear portion 110 (provided by the molded gear section 54) having four locking teeth aligned with four alternate teeth of the transfer gear 108.

With the higher order counter wheel 42 in its forward operative position shown in FIG. 4, its drive gear 106 is in mesh with the pinion transfer gear 108 and its locking ring 104 is positioned between the axially spaced gears 108, 110 and therefore clear of the pinion teeth. With the lower order counter wheel 40 in its forwardoperative position, its gear sector 102 is aligned for engagement with the transfer gear 108 for indexing the pinion 90 during each transfer for indexing the counter wheel 42 one full count (i.e., 36) for each revolution of the wheel 40. Also, with the wheel 40 in its forward operative position, the locking ring 100 is aligned for engagement with the locking gear 110 for locking the pinion 50 between transfers and the locking ring 101 is positioned between and therefore clear of the axially spaced gears 108, 110. In a conventional manner the locking ring 100 has a suitable tooth recess 118 in axial alignment with the tooth recess between the two teeth of gear sector 102 for receiving a tooth of the locking gear 110 for unlocking the pinion 50 during the transfer interval. In contrast the locking ring 101 has a 360 locking shoulder to completely lock the pinion 50 against rotation when the wheel 40 is axially shifted by the corresponding knob 68 to reset the wheel. Also when the wheel 40 is axially shifted for resetting the wheel the gear sector 102 is disengaged from the transfer gear 108 to permit the wheel 40 to be rotated in either angular direction by the knob.

In similar fashion when the number wheel 42 is axially shifted by the corresponding knob 68 for resetting the wheel, the drive gear 106 becomes disengaged from the transfer gear 108 and the locking ring 106 provides for locking the pinion 50 against rotation, thereby permitting the number wheel 42 to be reset in either angular direction while maintaining the pinion 50 locked against rotation. Consequently each number wheel 40, 42 may be individually manually reset in either angular direction by the respective knob without affecting the setting of the other number wheel.

The predetermining counter is adapted to be indexed in stepwise fashion in the subtractive direction by an electromagnetic operator 120, and a signaling mechanism 122 is provided for generating an electrical signal when the counter reaches zero. The signaling mechanism 122 comprises a suitable SPDT switch 124 mounted on the base portion 18 and a pivotal operating bail 128. The bail 128 has a pair of integral trunnions 129 received in sockets formed by the frame sections 14, 16 and rearwardly extending finger 130 engageable with a switch operating level 131 for holding the lever down until both numeral wheels 40, 42 reach their positions The bail has a pair of depending triangular followers 132 which ride on the hubs 82, 84 of the number wheels, and the hubs 82, 84 have V-shaped axial slots 133, 134 for receiving the followers 132 when the number wheels are in their 0 position. The bail 128 is thereby released for pivotal actuation by the switch lever 131 to provide for operating the switch 124 to generate a suitable electrical signal.

The electromagnetic operator 120 comprises a generally F- shaped laminated core 135 mounted upon reduced intermediate portions of the three rearwardly extending posts 24-26. A coil subassembly comprising a coil 126 wound upon a one-piece molded plastic bobbin 138 is mounted on the center leg 139 of the laminated core and a clapper 140 is mounted within a slot 141 in the core for pivotally supporting the clapper for pivotal movement (about an axis parallel to the axis of the shaft 44) for being attracted against the bias of a tension spring 142 when the coil 126 is energized. A pair of upstanding posts 146 are integrally formed on the plastic bobbin 138 for retaining the antiresidual pad 147.

A verge 150 is mounted on the outer free end of the clapper 140 and has a pair of opposed pawls 151, 152 for engagement with the star wheel 48 for indexing the wheel 40 a first substantially one-half count upon the energization of the coil 126 and the remaining substantially one-half count upon the succeeding deenergization of the coil 126. An elongated slot 154 is provided in the outer end of the clapper and the verge 150 has a supporting shoe 156 mounted within the slot 154 to provide for reciprocable movement of the verge along an axes extending transversely of the axis of the star wheel shaft 44. Also the verge 150 has a web 160 with an elongated locating slot 161 receiving the shaft 44 and designed for orienting the pawls 151, 152 relative to the star wheel 48 such that the floating verge support and the locating slot 161 together ensure proper orientation of the verge pawls 151, 152 relative to the star wheel 48 irrespective of the exact position of the remaining parts of the electromagnetic operator 120.

Referring to FIG. 3 the verge 150 and star wheel 48 are related such that when the resetting knob 68 for the wheel 40 is depressed, the star wheel 48 is axially shifted to disengage it from the verge 150 to free the wheel 40 for rotation in either angular direction. The verge pawl 151 and the hub of the star wheel 48 have suitable opposed tapered edges to avoid any hangup between the star wheel 48 and verge pawl 151 when the knob 68 is released.

The core 135 comprises a stack of five laminations -174 which are pinned together and preassembled with the bobbin subassembly and the clapper and verge and then installed on the reduced intermediate portions of the posts 24-26 (and the star wheel 48 is thereafter press fit on the shaft 44). The core 135 has a first relatively small opening 176 for snugly receiving the reduced intermediate portion of the post 25 and two relatively large openings 180, 181 for loosely receiving the posts 24, 26. Accordingly the core 135 can be pivotally adjusted on the post 25 to establish an air optimum airgap between the clapper 140 and the leg 139 of the core, it being desired to establish the minimum airgap which provide adequate pivotal motion of the verge 150 for indexing the number wheel 40.

An L-shaped nonpivotal lamination 186 having relatively small openings 188, 189 for receiving the posts 25, 26 is mounted on the core 135 and suitable nuts 190 are threaded upon the posts 25-26 to secure the core subassembly to the frame. The nuts 190 are initially tightened against the outer lamination 186 sufficiently to hold the core 135 in place but to permit pivotal adjustment of the core 135 about the post 25.

For pivotal adjustment of the core, there is provided a circular bore 198 in the plate 186 and an elongated slot 200 in the core 135. An adjustment tool 204 having a shaft 206 with a diameter substantially equal to the width of the slot 200 and an enlarged eccentric 208 having a diameter substantially equal to the bore 198 can be inserted into the assembled parts as shown in FIG. 1 and rotated to provide for setting the airgap.

As will be apparent to persons skilled in the art, various,

jacent wheels of lower and higher order having a first transfer gear portion with an even number of equally spaced teeth engageable with the transfer gear sector and drive gear for generating transfers from the lower to the higher order counter wheel and a locking gear portion having locking teeth in alignment with alternate teeth of the transfer gear portion and engageable by the locking ring means for locking the transfer pinion between transfers, the improvement wherein the counting mechanism further comprises individual counter wheel resetting means for each counter wheel for individually axially shifting the counter wheel in one axial direction from an operative angular position thereof to a withdrawn position to respectively disengage the transfer gear sector of the lower order counter wheel and the drive gear of the higher order counter wheel from the pinionto permit the respective counter wheel to be reset, wherein the higher order counter wheel has locking ring means normally out of engagement with the pinion, and wherein the locking ring means on the higher and lower order counter wheels are mounted for engagement with the pinion-locking gear portion with the respective counter wheel in its withdrawn position for locking the pinion while each counter wheel is being reset.

2. In a counting mechanism according to claim 1 wherein the individual wheel-resetting means comprises a knob mounted for rotation and axial movement coaxially with the wheel, and engageable with the wheel for shifting the wheel in said one axial direction and for resetting the wheel when it is in its withdrawn position, spring means biasing the knob in the axial direction opposite to said one axial direction to a normal inoperative position out of engagement with the counter wheel, and knob-locking means preventing rotation of the knob in its normal inoperative position but permitting rotation of the knob when axially shifted sufficiently in said one axial direction to shift the counter wheel to its withdrawn position.

3. In a counting mechanism according to claim 2 wherein the knobJocking means provide for positioning the knob in any one of a plurality of angular positions corresponding to the full count positions of the respective counter wheel so as to ensure the counter wheel is in a full count position when it returns to its operative position.

4. in a counting mechanism according to claim 1 wherein the pinion-locking gear portion is axially spaced from the pinion transfer gear portion in said one axial direction, and wherein the locking ring means of said higher order counter wheel is positioned between the spaced gear portions of the pinion with the higher order counter wheel in its operative position.

5. In a counting mechanism having a plurality of counter wheels of ascending order mounted for rotation about spaced parallel axes, a transfer gear intermediate adjacent counter wheels of lower and higher order for generating transfers from the lower order counter wheel to the higher order counter wheel, a drive shaft, the lowest order counter wheel being fixed onto the drive shaft for being driven thereby and an electromagnetic operator operable for indexing the drive shaft for indexing the counter, the improvement wherein the counting mechanism further comprises individual counter wheel resetting means for the counter wheels for individually axially shifting the respective counter wheel in one axial direction from an operative angular position thereof to a withdrawn position to disengage the counter wheel from the intermediate transfer gear for permitting the counter wheel to be reset, and wherein the electromagnetic operator comprises a star wheel fixed onto the drive shaft, a pivotal clapper and a verge mounted on the clapper, the verge and star wheel being adapted to cooperate for indexing the drive shaft with the lowest order counter wheel in its operative position and the star wheel and verge being relatively displaced with the lowest order counter wheel in its axially withdrawn position to permit the lowest order counter wheel to be reset.

6. A counting mechanism comprising a frame, a drive shaft mounted on the frame, a counter wheel fixed onto the drive shaft, an electromagnetic operator connectedfor indexing the drive shaft, and means for angularly resetting the counter wheel, the improvement wherein the resetting means comprises a knob mounted for rotatable and axial movement generally coaxially with the counter wheel, spring means biasing the counter wheel and drive shaft in one axial direction toward the reset knob to shift the counter wheel and drive shaft in said one axial direction from a withdrawn inoperative position thereof where the drive shaft is disconnected from the electromagnetic operator, to an extended operative position thereof where the drive shaft is connected for being indexed by the electromagnetic operator and biasing the knob in said one axial direction to shift the knob to an inoperative position thereof axially spaced and disengaged from the wheel, the knob being adapted to be manually shifted in the opposite axial direction against the bias of the spring means to engage the knob with the wheel to shift the wheel in said opposite axial direction to its withdrawn position for resetting the wheel, the knob and counter wheel having cooperating means to provide for positive engagement of the knob with the wheel when the knob is axially shifted into engagement with the wheel for rotating the wheel with the knob for resetting the wheel, and the frame having locking means for locking the knob against rotation with the knob in its said inoperative position and permitting rotation of the knob with the knob axially shifted sufficiently in said opposite axial direction to shift the wheel to its withdrawn position. 

1. In a counting mechanism having a plurality of counter wheels of ascending order mounted for rotation about spaced-parallel axes, the adjacent wheels of lower and higher order comprising locking ring means and a transfer gear sector on the lower order counter wheel and a drive gear on the higher order counter wheel, and a transfer pinion intermediate adjacent wheels of lower and higher order having a first transfer gear portion with an even number of equally spaced teeth engageable with the transfer gear sector and drive gear for generating transfers from the lower to the higher order counter wheel and a locking gear portion having locking teeth in alignment with alternate teeth of the transfer gear portion and engageable by the locking ring means for locking the transfer pinion between transfers, the improvement wherein the counting mechanism further comprises individual counter wheel resetting means for each counter wheel for individually axially shifting the counter wheel in one axial direction from an operative angular position thereof to a withdrawn position to respectively disengage the transfer gear sector of the lower order counter wheel and the drive gear of the higher order counter wheel from the pinion to permit the respective counter wheel to be reset, wherein the higher order counter wheel has locking ring means normally out of engagement with the pinion, and wherein the locking ring means on the higher and lower order counter wheels are mounted for engagement with the pinion-locking gear portion with the respective counter wheel in its withdrawn position for locking the pinion while each counter wheel is being reset.
 2. In a counting mechanism according to claim 1 wherein the individual wheel-resetting means comprises a knob mounted for rotation and axial movement coaxially with the wheel, and engageable with the wheel for shifting the wheel in said one axial direction and for resetting the wheel when it is in its withdrawn position, spring means biasing the knob in the axial direction opposite to said one axial direction to a normal inoperative position out of engagement with the counter wheel, and knob-locking means preventing rotation of the knob in its normal inoperative position but permitting rotation of the knob when axially shifted sufficiently in said one axial direction to shift the counter wheel to its withdrawn position.
 3. In a counting mechanism according to claim 2 wherein the knob-locking means provide for positioning the knob in any one of a plurality of angular positions corresponding to the full count positions of the respective counter wheel so as to ensure the counter wheel is in a full count position when it returns to its operative position.
 4. In a counting mechanism according to claim 1 wherein the pinion-locking gear portion is axially spaced from the pinion transfer gear portion in said one axial direction, and wherein the locking ring means of said higher order counter wheel is positioned between the spaced gear portions of the pinion with the higher order counter wheel in its operative position.
 5. In a counting mechanism having a plurality of counter wheels of ascending order mounted for rotation about spaced parallel axes, a transfer gear intermediate adjacent counter wheels of lower and higher order for generating transfers from the lower order counter wheel to the higher order counter wheel, a drive shaft, the lowest order counter wheel being fixed onto the drive shaft for being driven thereby and an electromagnetic operator operable for indexing the drive shaft for indexing the counter, the improvement wherein the counting mechanism further comprises individual counter wheel resetting means for the counter wheels for individually axially shifting the respective counter wheel in one axial direction from an operative angular position thereof to a withdrawn position to disengage the counter wheel from the intermediate transfer gear for permitting the counter wheel to be reset, and wherein the electromagnetic operator comprises a star wheel fixed onto the drive shaft, a pivotal clapper and a verge mounted on the clapper, the verge and star wheel being adapted to cooperate for indexing the drive shaft with the lowest order counter wheel in its operative position and the star wheel and verge being relatively displaced with the lowest order counter wheel in its axially withdrawn position to permit the lowest order counter wheel to be reset.
 6. A counting mechanism comprising a frame, a drive shaft mounted on the frame, a counter wheel fixed onto the drive shaft, an electromagnetic operator connected for indexing the drive shaft, and means for angularly resetting the counter wheel, the improvement wherein the resetting means comprises a knob mounted for rotatable and axial movement generally coaxially with the counter wheel, spring means biasing the counter wheel and drive shaft in one axial direction toward the reset knob to shift the counter wheel and drive shaft in said one axial direction from a withdrawn inoperative position thereof where the drive shaft is disconnected from the electromagnetic operator, to an extended operative position thereof where the drive shaft is connected for being indexed by the electromagnetic operator and biasing the knob in said one axial direction to shift the knob to an inoperative position thereof axially spaced and disengaged from the wheel, the knob being adapted to be manually shifted in the opposite axial direction against the bias of the spring means to engage the knob with the wheel to shift the wheel in said opposite axial direction to its withdrawn position for resetting the wheel, the knob and counter wheel having cooperating means to provide for positive engagement of the knob with the wheel when the knob is axially shifted into engagement with the wheel for rotating the wheel with the knob for resetting the wheel, and tHe frame having locking means for locking the knob against rotation with the knob in its said inoperative position and permitting rotation of the knob with the knob axially shifted sufficiently in said opposite axial direction to shift the wheel to its withdrawn position. 